Java programs perform Input Output through streams. A stream is an abstraction that either produces or consumes information. A stream is simply a sequence of bytes that flows into or out of our program. It’s an abstract representation of an input or output device.

• A stream is linked to a physical device by the Java IO stream.

• All streams behave in the same manner even if the actual physical devices to which they are linked differ.

• Thus, the same IO classes and method can be applied to any type of decvice.

• This means that an input stream can abstract many different kinds of input:from a disk file, a keyboard or a network socket.

• Java implements stream within class hierarchies define in the java.io package.

Types Of Streams:

1. Byte or Binary Stream.

2. Character Stream.

Byte/Binary Stream :

• Byte stream provide a convenient means for handling IO of bytes.

• Byte streams are used for example, when reading and writing binary data.

• Byte streams are defined by using two class hierarchies:
  At the top are two abstract class

• java.io.InputStream and

• java.io.OutputStream.

• Each of these abstract classes has several concrete sub classes, that handle the differences between various devices.

• The abstract classes InputStream and OutputStream have several key methods, that the other stream classes implement.

• Two of the most important methods are read() and write(), which respectively read and write bytes of data.

• int read() throws IOException
  Returns the next byte available from the stream as type int. If the end of the stream is reached, the method will return the value -1.

• int read(byte [] array) throws IOException
  This method reads bytes from the stream into successive elements of array. The maximum of array.length bytes will be read.

• void write(int data) throws IOException

• void write(byte [] array) throws IOException

Character Stream :

• Character streams provide a convenient means for handling IO of characters.

• They use Unicode and therefore internationalized. Also, in some cases character stream are more efficient than byte stream.

• Character streams are defined by using two class hierarchies.
  At the top are two abstract class

• java.io.Reader and

• java.io.Writer.

• The abstract classes Reader and Writer several key methods, that the other stream classes implement.

• Two of the most important methods are read() and write().

• Methods for performing character based reading operation:

• int read( ) throws IOException

• int read(char [] array) throws IOException

• Methods for performing character based writing operation:

• void write(int data) throws IOException

• void write(char [] array) throws IOException

Standard Stream :

In java, 3 standard stream objects are implicitly available.

1. System.out : standard output stream,
Type: PrintStream,
Represents: system's console,

2. System.in : standard input stream,
Type: InputStream,
Represents: system's keyboard,

3. System.err : standard error stream,
Type: PrintStream,
Represents: system's console,